Our discovery of cytonemes, specialized filopodia that orient toward cells that express signaling proteins, suggest a novel mechanism to move signaling proteins between producing and target cells. This model postulates that signaling proteins move between cells in a manner similar to the way neurotransmitters move at neuronal synapses, that fundamentally, neurons and non-neuronal cells communicate in similar ways. Recent work from my lab now provides direct and convincing experimental evidence that cytonemes ferry signaling proteins between producing and receiving cells, strongly supporting the cytoneme model. Our work also identified several unexpected properties of cytonemes that have significant implications for mechanisms of signal transduction. The work proposed in this application will develop new tools for imaging cytonemes and will build upon our previous findings to determine the roles, composition and functions of these remarkable organelles. PUBLIC HEALTH RELEVANCE: When cells in a developing animal grow to form tissues and organs, they often do so in response to gradients of chemical signals, yet the precise mechanisms by which these molecular messages move and are received is not known. Our work has provided strong evidence that thin finger-like protrusions from cells known as cytonemes play a key role in this process. Research proposed in this application will explore the structure and function of cytonemes and will have important implications for cell-cell signaling in all animals and in many contexts.